Patent GB-388809-A (GB)
Title: Improvements in and relating to electric control systems employing electric discharge devices
IPC: H02J3/36
Filed: 1931-09-02
Abstract: 388,809. Control systems for consuming devices ; converting ; phase changing. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Bedford, B. D. ; 329, Germania Avenue, Schenectady, New York, U.S.A.) Sept. 2, 1931, No. 24684. Convention date, Sept. 2, 1930. [Classes 38 (ii) and 38 (iv).] A vapour electric discharge device, the anode circuit of which includes an alternating potential, is rendered substantially fully conducting by applying a relatively high frequency potential to its grid circuit and non- conducting when a variable negative grid bias exceeds the amplitude of the high frequency potential. The invention is applied in a system for alternately dimming and brightening simultaneously the lamps in two different circuits. The discharge device excites the high frequency potential and charges a condenser which through a resistance controls the rate of current changes in the lamp circuits. A vapour electric discharge device 55, Fig. 3, connected to an alternating current source 32 sets up oscillations in a circuit 58, 60, connected by condensers 57, 59 across a resistance 56, whilst the device is conducting. The high frequency potential is applied through a potentiometer resistance 41 to the grid of the device 55. Two load circuits 30, 31 are controlled by choke coils 33, 34 saturated periodically by the current from rectifying valves 36, 37 and 39, 40 respectively, which are preferably of the vapour type. The conductivity of each of these pairs of valves is controlled in opposite senses by potential applied to their grids by circuits 20, 21 respectively. The resistance 41 is in series with one pair of valves and is the seat of a varying negative bias for the grid of the valve 55. When the current in the valves 39, 40 reaches a maximum value and the lamps 31 therefore maximum brightness this negative bias exceeds the amplitude of the high frequency potential and the valve 55 ceases to conduct. A condenser 52 is connected through a variable resistance 53 to the terminals of the resistance 56. It is charged during the conducting periods of the valve 55 and discharges in the intervals. In so doing it varies the conductivity of valves 50, 51 arranged to short circuit the secondary of a transformer 49 whereby its primary winding acts as.a continuously varying resistance. This transformer winding forms part of a phase shifting circuit supplying the circuits 20, 21 with grid control voltages, as shown in Fig. 1, wherein the variable resistance 14 replaces the transformer winding. The source 12 supplies a resistance 10 and a reactance 11 in series. The circuits 20, 21 are connected as shown to the resistance 10 and a transformer 15, the primary winding of which receives an out-of-phase voltage from the reactance 11 which is varied and reversed by the changing value of the resistance 14 which is connected in series with a resistance 13 across the reactance. The mutually reversed voltages of the secondaries of the transformer 16 are compounded with the in-phase voltage from the resistance 10 to produce in the circuits 20, 21 voltages equal in magnitude and changing in phase simultaneously but in opposite senses. This phase change is repeatedly reversed by the action of the condenser 52, Fig. 3. The transformer primary may be across the portion 19 of the resistance 10 instead of as shown. The resistances 13, 14 may be replaced by any other impedance bridge.